Since President Obama took office, the Democratic advantage in voter identification – including those who call themselves independent but lean Democrat – has shrunk each quarter, to the point where the gap is only 6 points, the smallest since 2005, according to the latest Gallup poll. In the first quarter of 2009, when Mr. Obama took office, the gap was 13 points and in the second quarter, 9 points, per Gallup.

Among those who identify with a party, 35 percent are Democratic and 13 percent lean Democratic. Republican identifiers are 27 percent and an additional 15 percent lean Republican. The good news for Democrats is that the Republicans have not gained among adults who are willing to identify with their party. That number has held steady in the high 20s since 2006. And Democrats have held steady in the mid-30s for nearly two years.

The play is among independents – and that’s where the Republicans are picking up steam. These numbers hold big implications for the 2010 midterm elections, when the party controlling the White House typically loses congressional seats.

Gallup attributes the shift to the healthcare debate and fiscal concerns.

“Gallup has found that independents are more likely to oppose than support healthcare reform, and to express concerns about increased government spending and the expansion of government power,” writes Jeffrey Jones of Gallup. “Thus the drop in Democratic support is partly a response to concerns about the policies Obama and the Democratic Congress are pursuing.”

The all-time high in the party ID gap, including leaners – 14 points – was reached in both the fourth quarter of 2006 and the first quarter of 2008. Gallup has been measuring what it calls “leaned party identification” since 1991.